Soil fungicide



3,080,274 SfiIL FUNGICIDE Marvin Legator, William A. Kreutzer, and Samuel B. Soloway, Modesto, Calih, assignors to Shell Oil Com- 3,080,274 Patented Mar. 5, 1963 five dosages in the form of water solutions or acetonewater emulsions after the soil was planted. Readings on seedling rot damping off of sugar beet seedlings were made at fiveand ten-day intervals.

pany, New York, N.Y., a corporation of Delaware 5 Nabam, TMTD and Captan controlled Pythium pre- No Drawing. Filed Feb. 10, 1960, Ser. No. 7,780 emergence at the highest levels only. The trimethyl phos- 6 Clmmsphorothioate was clearly superior to all other fungicides This invention relates to the employment as a soil 111 the control of Pyihillm f mlmtfungicide of 0,0,0 trimethyl phosphorothioate, In order to l y estabhsh the supenor flmslcidal (CH O) PS, and to novel fungicidal compositions con- 10 P p f trlm thyl phosphorothiolate, a test was taining this compound. This application is a continua. made under field conditions. Parallel tests were simultion-in-part of application No. 719,511, filed March 6, Y made, using the three d iflna Ch micals '1958, now abandoned. It has been found that 0,0,0- noted 1n the table below. These three chemicals were trimethyl phosphorothioate manifests a highly selective selwted 5111c? y F structurally l0 lil'imellhyl fungitoxic action toward soil pathogens of the Pythium 5 Phosphorothloate eXcept for the l atlon and intertype hil not fl i plants, change of sulfur and oxygen atoms in the various possible O,(),O-t i th 1 h h hi may b d b h positions. The exhibited superiority over these closely addition of sulfur to .trimethyl phosphite or by the rea d Chemicals along Wlth the p f y di SC 11SSed action of thiophosphoryl chloride with sodium methox- P OVeI' hmjlologs and f f funglfildes p y ide. Thus in one preparation of 0,0,0-trirnethyl phosillustrate the unlque and Sul'PnSmg PYOPGIUCS 0f phorothioate, 32 grams of sulfur was added during the Y P P Course f 20-30 i t to 137 grams of i fl l 1 In this test the chem1cals were apphed as coarse aqueous phite, maintaining a temperature of 55-60 by means of B Y i surface of S011 Planted Wlth Sugar beet Seedan ice bath. The yellow solution was stirred at 60 for 11131 Yeadlngs were made 18 and days after the p 15 minutes after the final addition of sulfur, filtered and 25 m and treatment date- Results w r s follows: distilled to yield 98.0 grams of 0,0,0-trimethyl phosphorothioate boiling at 66-9 at 10 mm.; n 1.4572. Grams Average Average The outstanding fungicidal activity of 0,0,0-trimethyl C i al Cheri lica l P e rgent Pe rpent phosphorothioate is quite surprising in view of the fact 233g g' ff 3 3; that structurally similar compounds such as 0,0,O-tr1- 0 ethyl phosphorothioate and O ,0,0-tributyl phosphoro- Untreated control 2,7 25 thioate have been found relatively ineffective. m t ylt trathiophosn a 8.2 g g This altogether unexpected superiority of 0,0,0-tri- 0 0 methyl phosphorothioate as a soil fungicide is illustrated 0.1 0 0 by the following experiment in which the triethyl and 5 Tnmethylphosphate 8:2 1;; tributyl homologs were compared with the trimethyl com- 8.? 19.3 pound. The tests involved sugar beet attack by Pythium. Trimethyl phosphorotrithioite 10'?) 2 012 3115 2715 Minimum Dose in MilJi- 0.1 45. 0 23. 7 grams Giving 40 Trimethyl phosphorothioate 0.8 47.5 45.0 0.4 57.5 65.0 0.2 60.0 67.5 Complete Phyto- 0. 1 100. 0 100. 0

Disease toxicity Control 1 Based on estimation of a perfect seedling stand. ,8,- i g p gt i p 3-23 2-8 Analysis of the data indicates that trimethyl phosgfi f figi ;,fj;j 5 1 phorothioate has a control level less than 0.1 gram/foot while trimethyl tetrathiophosphate was not effective at any Not only is 0,0,O4rimethy} phosphorothioate vastly dosage in this field test. Trimethyl phosphorotrithi oite superior to its homologs as a soil fungicide against 50 gave only poor control at the dosage of least phytotoxrcity Pythium but it also appears superior to various com- (odfimm) exhlblted P P was Phytotoxlc mercial fungicides tested in accordance with the followat hlghef dosages 413 gram). Trimethyl phos hate mg procedure gave poor control at any dosage, the drop n stand at Screened soil was steamed in order to sterilize it and the 04-08. gram levels mdlcatlpg phytotoX1c1.tY' th derb r tel infe ted Wim cultures of P thium 0,0,0-trrmethyl phosphorothio-ate shows highly seleci was s 1 y s t 25 200 z tubes tive action against Pythium as evidenced by the followu i i' 26ml) es i 31 dd (1 at ing test. Pythium is a genus of fungi (family Pythiaceae) contammg 7 grams 0 S01 mm 8 were e which consists of facultative parasites and is frequently important as a root parasite. A culture of Pythium i i z g g lgfig ultimum was isolated and the test chemical run against Pythium Oontrolofthis organism as well as against other soil pathogens Funglclde under in vitro conditions. The following results were Pre- Postobtained. emergence emergence Attack Attack 65 Concen- Tetramethyl thiura disulfide (TMTD) 3.0 3.0- 3.0 a m ifiratloi'ln Growth Disodium ethylene bis dithiooarbamate P-P- (Nabam) 3.0 3.0 'l gg og g t lt e a hrdrophthahmlde 3 0 3 0 Pythmm ultimum 30 None. pena hiorasazarin"(reins 115 320 gadoliniumalboatmmn-fl it? Equimmml' Trimethyl phosphorothioate -2 ZJZZ$ ZfS KTZII ggi o.

Dosage test range was 3.0, 1.5, 1.0, 0.5 and 0.25 milligrams.

Because phytotoxicity is a critical factor in evaluating a soil fungicide, extensive phytotoxicity tests were conducted on sugar beet seeds. Tolerance was found to be as high as 1-2 grams/square foot of soil. Tomato and beet .seedlings show no apparent injury at 0.25 gram/ square foot of soil Pea seedlings appear to tolerate dosages as high as 0.75 gram/square foot of soil without undue injury. These tests also indicate that no phytotoxic residue is left in soils fol-lowing excessively heavy doses of 0,0,0-trimethyl phosphorothioate.

The following test shows the high order of activity of this chemical as well as a 10-20 fold range of control without causing phytotoxicity.

Concentration of O, O, O-trimethyl Phytotoxicity phosphorothioate in Grams/Tube e Control (Sugar Beet of Soil Seedlings) .005 Complete. Slight.

.002; d None.

.001 .do Do.

0005; "do Do.

' a Each test tube contains approximately 70 grams of soil.

These tests indicate that 0,0,0-trimethy1 phosphorothioate is highly selective against Pythium and comparatively non-toxic to plants.

Seed treatment with 0,0,0-trimethyl phosphorothioate controls Pythium pre-emergence rot. A talc dust containing 10% w. of this compound may be used to control Pythium even when the dust is merely sprinkled on the surface of wet planted soil at the rate of 0.24- gram/ square foot. The material is quite effective either as an aqueous surface drench at the time of planting or as a dry soil mix pre-planting treatment. This compound has also been found to stop or retard attack by established Pythium when added to the surface of the soil following seed germination.

In order to establish the value of 0,0,0-trimethyl phosphorothioate as a therapeutant, that is, as a cure for plant disease \which has already become established, the following test was conducted. Beet seeds were treated with tetramethyl thiuram disulfide (Thiram) for the purpose of controlling pre-emergence attack. Both treated and non-treated seeds were planted at one-half inch levels in standard 25 x 200 mm. tubes. Aqueous drenches at varying doses of 0,0,0-tn'methyl phosphorothioate were added either at the time of emergence or after emergence at the first appearance of post emergence attack. Control was brought about in all cases.

Secondary Treatment Seeds Treated with Seeds not treated Thiram 0,0,0trirnethyl phosphorothioate aqueous drench at time of emergence (4 days).

0,0,0-trimcthyl phosphorothioate aqueous Normal stands Postemergence attack controlled by 0.3-1.0

mg. Normal stands Postemergence e attack N stand; complete emergence rot.

drench at first sign of controlled by 0.3 post emergence attack mg. (8 days). N o secondary treatment- Normal stands; partial No stand; complete post-emergence pre-emcrgence rot. damping ofi".

Pythium ultimum attack.

phorothioate which shows a marked specificity for Pythium may be employed with the known soil fumigant, PCNB, pentachloronitrobenzene, which shows a marked specificity for Rhizoctonia. Wetting agents, and if neces sary or desirable, stickers such as the heavy hydrocarbon oils @with a minimum viscosity of 10 Engler at 50 C. can be present. The wetting agent must be non-reactive with the phosphorothioate. If the phosphorothioate is employed in the form of emulsion or suspension, for example, in water, solvents such as oils, emulsifiers, emulsion stabilizers, and the like may be added.

The phosphorothioate of the present invention may be applied :by spraying. Spraying of plants may be performed with aqueous emulsions, solutions or suspensions. The spray liquid is generally applied at a rate of from about 7.5 to gallons per acre. If spraying is efiected with smaller quantities of liquid as in low volume spraying, high concentrations of the phosphorothioate should be employed. If desired, a minor amount of the order of about 0.0 1 to about 0.05% by weight, of a wetting agent may be added to aid in forming a suspension. Particularly suitable wetting agents are the sodium salts of a mixture of secondary heptadecyl sulfates, sold commercially under the name of Teepol and polyethylene glycol ethers of alkyl phenols sold under the trade name of Triton X-11O0 and Triton X-al55. Preferable concentrate compositions comprising the phosphorothioate of the present invention and a suitable wetting agent are prepared, and the concentrate is then dispersed in water prior to use.

A further form in which the fungicidal compound of the present invention may be applied consists of 'solutions of the active ingredient in suitable inert liquid or semi-solid diluents, in which the phosphorothioate is present in molecularly dispersed form. The form in which the phosphorothioate is employed depends on the subject and purpose of the application.

Suitable inert solvents for the manufacture of liquid preparations should not be readily flammable, as odorless as possible and without any toxic elfect on humans and animals when properly used. Neither should they have a corrosive effect on the components of the preparations or the material of the storage vessel. Examples of suitable solvents are high-boiling oils, e.g., oils of vegetable origin such as castor oil, etc., and lower boiling solvents with a flash point of at least 30 C., such as carbon tetrachloride, ethylene dichloride, acetylene tetrachloride, hydrogenated naphthalene, alkylated naphthalene, sorbcnt naphtha, etc. Mixtures of solvents may also be used. Non-aromatic petroleum oils and xylene are commonly employed.

This compound may also be employed in the form of aerosols. 'When so used the phosphorothioate is dissolved, or dispersed in a solvent boiling below room temperature at atmospheric pressure.

0,0,0,-trimethyl phosphorothioate may also be applied in the form of dusts utilizing as the inert vehicle such materials as tricalcium phosphate, precipitated chalk, bentonite, kaolin, kieselguhr, etc.

It has been found that activated carbon is a most satisfactory inert vehicle for the formulation of such fungicidal dusts. -Any of the various types of activated carbon may be used. For example, activated carbon obtained from the carbonization of plant raw materials, from charcoal formed "by steeping the raw material in zinc chloride, or by mixing the raw material with carbonates such as calcium carbonate are all suitable as the inert vehicle. It is prefer-red to use Columbia activated carbon for this purpose.

A trimethyl phosphorothioate-activated carbon dust is attended by a loss of the trimethyl phosphorothioate with the passage of time. This instability has been an economic drawback to this formulation as well as a problem in storage when the dust was not to be promptly used after formulation.

By means of infrared analysis of CS extracts of the trimethyl phosphorothioate-activated carbon dust at various proportions over a period of 20 days, it has now been discovered that when the trimethyl phosphorothioate is present in the dust in concentrations of up to approximately 40% by weight, the loss of trimethyl phosphorothioate is very much reduced over that at higher concentrations. Therefore, the fungicidal dust comprising activated charcoal and up to approximately 4( by weight of trimethyl phosphorothioate is preferred when a dust formulation is desired. If this preferred embodiment is utilized, the percent loss in storage will be relatively low with a resulting monetary savings.

The method of application may vary considerably without departing from the scope of the invention. Thus the phosphorothioate may be applied to the entire area of "a field. This procedure is called solid, or broadcast, application. The chemical may also be applied in rows or hills Where the plants are to grow. It is preferable to inject the soil fungicide at uniform depth. However, it is also possible to apply the chemical as a surface treatment when mixed with water or with a powder carrier. When mixed with a higher boiling point diluent the chemical may be injected into the soil. The chemical may be pre-mixed with the seeds or applied as part of the seeding operation if desired. Other methods of application will also be apparent to those versed in the art, it being understood that the methods of application are not limited to those specifically enumerated.

We claim as our invention:

1. The method for protecting a living plant from attack by Pythium fungi which comprises introducing into the o soil comprising the rhizosphere of the plant an effective dosage of 0,0,0-trimethyl phosphorothioate.

2. The method for protecting viable seed and the plant sprouting therefrom from attack by Pythium fungi which comprises applying an effective dosage of 0,0,0-trimethyl phosphoro-thioate to seed prior to the time the seed is planted.

3. The method according to claim 2 wherein the 0,0,0-trimethyl phosphorothioate is applied in the form of a dust.

4. The method for overcoming attack by Pythium fungi and preventing further attack by said fungi comprising introducing into the soil comprising the rhizosphere of the plant undergoing attack by Pythium fungi an effective dosage of 0,0,0-trimethy-l phosphorothioate.

5. The method for protecting viable seed and the plant sprouting therefrom from attack by Pythium fungi which comprises introducing into the soil in which the seed is to be planted, and within a short time before the seed is 20 planted, an effective dosage of 0,0,0-trimethyl phosphorothioate.

6. A fungicidal dust comprising activated charcoal and up to approximately 40% by weight of trimethyl phosphorothioate.

References Cited in the file of this patent UNITED STATES PATENTS Scott Nov. 18, 1958 OTHER REFERENCES 'Metcalf: Advance in Pest Control Research, pp. 227- 228 and 232, vol. '1, June 1951. 

1. THE METHOD FOR PROTECTING A LIVING PLANT FROM ATTACK BY PYTHIUM FUNGI WHICH COMPRISES INTRODUCING INTO THE SOIL COMPRISING THE RHIZOSPHERE OF THE PLANT AN EFFECTIVE DOSAGE OF O,O,O-TRIMETHYL PHOSPHOROTHIOATE. 